1. Field of the Invention
The present invention relates to a liquid crystal display element in which an auxiliary capacitance electrode is arranged so as to overlap with a thin-film transistor.
2. Description of the Related Art
In recent years, an active matrix crystal display element using a thin-film transistor (TFT) as a switching element has been developed. In the active matrix type liquid crystal display element, an auxiliary capacitance is formed to hold a display signal voltage written in a pixel electrode until the next write timing. This auxiliary capacitance is formed by an auxiliary capacitance electrode arranged to interpose an insulating layer between the auxiliary capacitance electrode itself and a pixel electrode.
Meanwhile, in configurations that an inversely-staggered structure (a bottom gate structure) is adopted for a thin-film transistor, to avoid light leak that occurs due to light entering from a liquid crystal layer side toward the thin-film transistor, a structure that an auxiliary capacitance electrode also functions as a light shielding film for the light has been known (e.g., JP-A 2004-341185 (KOKAI)—FIG. 5). That is, a structure that the auxiliary capacitance electrode made of a metal having light shielding properties such as chrome or molybdenum is formed between a source/drain electrode layer and a pixel electrode layer so as to overlap with a thin-film transistor has been known.
However, since the auxiliary capacitance electrode is formed as a film on a flatly formed insulating layer by, e.g., a sputtering method so that a lower surface of the auxiliary capacitance electrode is in contact with the insulating layer, the lower surface of the auxiliary capacitance electrode is disadvantageously formed as a mirror finished surface.
Therefore, in lights traveling toward the liquid crystal layer from a substrate side having the thin-film transistor formed thereon, light traveling toward the auxiliary capacitance electrode through a position near the thin-film transistor is reflected by the auxiliary capacitance electrode while maintaining a high light quantity, and this reflected light enters a semiconductor layer of the thin-film transistor even in an inversely-staggered configuration, whereby a light leak current is generated between a source electrode and a drain electrode.